In recent years, as semiconductor devices become smaller in size and denser, flip chip packaging has received attention and been spreading rapidly as a technique for mounting a semiconductor chip to a circuit board. In the flip chip packaging, it is common to employ bonding a semiconductor chip to a circuit board using a resin composition as a method for securing the electrical connection reliability at a joint of metal electrodes. Examples of the bonding method using a resin composition include a method in which a pasty resin composition containing a solvent is applied to the surface of one of bonding objects, and the solvent is removed, after which heat and pressure is applied to bond the bonding objects and at the same time harden the resin composition, and a method in which a pasty resin composition is applied to an exfoliative substrate in advance, and then a solvent is removed to produce a resin sheet, which is used to bond bonding objects. In manufacturing a build-up multilayer board in which conductor layers and insulating layers are alternately laminated, the resin composition may also be used a the insulating layers in the form of a hardened resin composition. Such resin compositions are being frequently used in various applications such as electrical and electronic applications, building applications, automotive applications, and aircraft applications (see, for example, Patent Documents 1 to 2).
The above resin sheet is designed such that it does not have adhesion at room temperature in view of handleability at room temperature but softens to exhibit adhesion when heated to about 100° C. When softened by heating, the resin composition constituting the resin sheet preferably has a low melt viscosity. However, the resin sheet has the disadvantage of gradually hardening during storage and increasing its melt viscosity, and an improvement in storage stability has been demanded. To this problem, techniques are disclosed for improving the storage stability at 100° C. or lower by using a microcapsule type hardening acceleration agent (see, for example, Patent Documents 3 to 4).
In addition, there is a problem in that the hardened resin composition greatly expands and contracts with changes in temperature, producing a stress inside the resulting semiconductor device, which results in reduced reliability of the device. To this problem, techniques are known to add inorganic particles into a resin composition in order to bring the coefficient of linear expansion of the hardened resin composition close to low coefficients of linear expansion of a semiconductor chip and a circuit board (see, for example, Patent Documents 1 to 4).